Nicholas C. Zakas wrote:
Thanks for the clarifications. I understand wanting to make the
distinction from an implementer point of view, I'm just not sure that
developers make the distinction between [[Put]] and
[[DefineOwnProperty]] even using regular object literals. Is there a
reason that this:
var obj = {};
obj.{
name: "JS"
};
Can't act the same as this:
var obj = {};
obj.name = "JS";
Wherein, if the property is already defined that acts as [[Put]] and
otherwise acts as [[DefineOwnProperty]]?
There's a big reason, which came up recently as if it were still
exploitable in modern browsers (fixed in 2009 era, at least in Firefox):
http://fafadiatech.blogspot.de/2012/04/json-hijacking.html
SpiderMonkey bug fixed in 2009:
https://bugzilla.mozilla.org/show_bug.cgi?id=474501
Note that the modern DOM and WebIDL are being spec'ed so typical DOM
accessors are on prototypes, so you can't "fix" the bug by using [[Put]]
only when the property is "own".
There really is a difference between assigning and defining in JS.
Assigning runs setters, even inherited ones. Defining overrides or
shadows. EIBTI.
/be
Thanks,
Nicholas
On 5/28/2012 2:27 PM, Allen Wirfs-Brock wrote:
On May 28, 2012, at 1:23 PM, Erik Arvidsson wrote:
On Mon, May 28, 2012 at 12:19 PM, Nicholas C. Zakas
<[email protected]> wrote:
Is it intentional that the first example uses colons between the
property
and value while all others use the equals sign?
Yes this is intentional. We discussed this a bit at the F2F meeting
and we came up with the proposal to use = for [[Put]] and : for
[[DefineOwnProperty]]. Having a way to do [[Put]] is important because
it is common to want to trigger setters.
At added a clarification of this to the strawman....
For example:
class Monster {
set health(value) {
this.barColor = value< 10 ? 'red' : 'green';
this._health = value;
}
}
class GiantSpider extends Monster {
constructor() {
this.{
health = 100
}
}
}
If you use .{health: 100} then the setter would not be invoked and the
object would not be in a correct state. This example might be a bit
contrived but using [[DefineOwnProperty]] is not the right answer in a
lot of cases.
This is especially important for setting values of DOM node
properties which are generally implemented as accessor properties
(ie, getters/setters). That is why I used (thanks to dherman) a DOM
element in most of the example that use +.
Allen
_______________________________________________
es-discuss mailing list
[email protected]
https://mail.mozilla.org/listinfo/es-discuss
